Does the Pill Make You Slower?

If you take an oral contraceptive, you might have wondered if that little pill could influence your running. Recently, the topic surfaced in the running news when Olympic hopeful Stephanie Bruce announced a surprise pregnancy, and told Runner's World that she's never been on birth control because "it has a lot of extra effects on running."

But what exactly are those effects, and have they been proven? A topic that affects so many women—a 2008 study found that more than 80 percent of female elite athletes took some form of birth control pill—certainly deems careful consideration. So we looked at the science, and talked with University of Florida obstetrician/gynecologist (and avid triathlete) Sharon Byun, M.D., to find out what women should know about contraception and competition.

Limited Research
There aren't a lot of published studies that have looked at the effects of hormonal birth control on running performance or speed—partly because it's a very hard thing to gather accurate data on.

"Every runner is different and every run is different, and in a clinical trial it would be very difficult to say whether someone's performance on any given day was affected by their birth control or any number of other things," said Dr. Byun.

Of the research that has been done, some suggests that birth control use may have small negative effects on things like strength gains, Vo2 max, and aerobic capacity in elite athletes. But other studies haven't backed up these claims—and none have actually looked at speed as an outcome.

Dr. Byun is unconvinced that slight decreases in these types of performance measures would have a significant influence on a woman's 5K or marathon time. And she doesn't recommend reading too much into studies that suggest they might.

"If I were an elite runner taking birth control and I read that it might affect my Vo2 max, what is that going to do to me psychologically?" she said. "When it comes to elite performance, what you believe about your body can make a big difference."

Potential Benefits
Preventing an unplanned pregnancy is the most obvious benefit of birth control pills. But birth control can also help relieve painful cramps and lessen heavy periods—factors that could very well keep a woman from performing at her best. Some women who have heavy bleeding can even become anemic, and feel weaker and more sluggish, while they're menstruating.

"For some women, nothing is more annoying and stressful than dealing with a heavy or painful period when they're trying to compete at a high level," said Dr. Byun. Some runners may even choose to skip their periods entirely if they overlap with important races, by foregoing their week of placebo pills.

Runners who have or are at risk of female athlete triad syndrome may also be on birth control to protect them against injuries like thinning bones and stress fractures. In cases like these, Dr. Byun said, these big-picture benefits likely outweigh any marginal changes that may occur in performance measures.

Is Weight Gain a Factor?
One thing that can affect a runner's speed is her weight: All other things being equal, she may run a couple seconds slower per mile for every extra pound she carries over her ideal weight. And because birth control is sometimes blamed for weight gain, women may wonder whether there's a connection to speed, as well.

But in the largest and most well-done trials, combination estrogen and progestin contraception (the most popular type of birth control pills) have had no effect on weight gain over time.

The only modern-day birth control that has been linked to increased weight is progestin-only forms, like the injectable Depo-Provera. "There might be some potential weight gain with these, but it would be similar to what a woman might experience naturally every month—fluid retention and bloating right before she got her period, when her progestin levels are highest—if she weren't on birth control," Byun said.

Find Out What Works for You
Overall, Dr. Byun believes that the Pill's benefits likely outweigh any potential drawbacks for most runners—elite or recreational. Pretty much any contraceptive on the market contains a very low dose of hormones (unlike women's earlier options in the 1960s and 70s), she said, and they've shown to be effective at preventing pregnancy without many side effects.

Still, every athlete needs to decide for herself. "It's the same with any aspect of training," she said. "We all want to know what the so-called best nutrition plan is, but not everyone is going to do well with paleo and not everyone is going to do well with gluten-free. Every body is different, and you need to figure out what works for you."

Even if there were high-quality clinical trials on the topic of birth control and running, she still says the results may not be generalizable to a wide population of people. "You're going to get individual effects regardless of how robust the evidence," she said. "Honestly, the best study is going to be the one you do on yourself."

If you're really curious, you can do just that—a study on yourself. The wash-out period in which birth-control hormones leave the body is just a few weeks, Dr. Byun explained. "Take the Pill for a few months and record your times, then stop taking it and, a month later, test yourself again."

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